Period value measurement
In addition to the counter value the period value can also be calculated and output. The following limit values apply to the determination of measured values:
Measured value output | Measured value limit | Comment | |
|---|---|---|---|
lower | top | ||
Period value | 0.20 µs | 21 s | with 4-fold evaluation, Signal type: RS422 (diff. input) |
1 µs | 21 s | with 4-fold evaluation, Signal type: TTL (single ended), open collector | |
Period value measurement sequence (Period value)
- For the period value measurement, the time between two positive edges of input A is measured with a resolution of 10 ns.
- In each case the last period within the PLC cycle is considered and output as separate process data in index 0x60n0:14 "Period value".
- "Period scaling" (index 0x80n0:14) indicates the resolution of the output period value. The default value is 10 ns. Alternatively the period value can be output in the unit 100 ns (0x80n0:14 "Period scaling" set to 100dec) or 500 ns (0x80n0:14 "Period scaling" set to 500dec).
- If no full period is detected within a PLC cycle (two positive edges of input A), the last valid value is output.
- The period measurement continues across cycles. As soon as a new value is available, the process data is updated in index 0x60n0:14"Period value".
- If no full period is detected within 21 seconds, the measurement is discarded and the output in index 0x60n0:14"Period value" is set to the maximum value, 2147483648.
Fig.169: Period value measurement
Fig.170: Period value measurement for long periods | Difference frequency and period value measurement The period value is recalculated for each cycle and output in the process data. The frequency measurement always averages the measured periods over a timeframe. The "Period value" is therefore a current value, the "Frequency value" is an averaged value. |